Mixing detector circuit for detecting frequency-modulated oscillations



Nov. 28, 1950 A. J. w. M. VAN OVERBEEK 2 5 MIXING DETECTOR FOR DETECTING FREQUENCY -MODULATED OSCILLATIONS f Filed Jan. 6, 1948 INVENTOR. ADRuwus TQHANNES WILHELMU MAME VAN OVEKBEEK AszNT Patented Nov. 28, 1950 UNITED STATES PATENT OFFICE MIXING DETECTOR CIRCUIT FOR DETECT- ING FREQUENCY-MODULATED OSCILLA- TIONS Application January 6, 1948, Serial No. 732' In the Netherlands January 14, 1947 fi'Glaims. 1,

In a known converter tube detector circuit for detecting frequency-modulated oscillations, the oscillations to be detected are supplied to two coupled circuits, the second of which is tuned to the central frequency of the said oscillations. The voltages generated across the two circuits exhibit a phase-shift dependent on the frequencies of the oscillations to be detected. These voltages are supplied to two control grids of a mixing tube so that the anode circuit of this tube is traversed by a current having a low-frequency component which, to a first approximation, is proportional with the frequency deviation of the oscillations to be detected.

The'object of the present invention is to provide a mixing detector circuit the operation of which is based on a different principle, but which also comprises a tube having two control grids. It affords the advantage that simpler circuit elements will sufiice (notably there is no need for utilising two coupled circuits) while the sensitivity and the linearity satisfy high requirements.

According to the invention, in a mixing detector circuit including a tube having at least two control grids, the oscillations to be detected are supplied to the first of the two said control grids, which grid is operated in class AB or class B condition. There is derived from another electrode and/or an auxiliary tube, by means of a retarding network, a pulsatory voltage which is supplied to the second control grid in such manner that, a constant time after the passage of current by the first grid, the second grid operating in class B or class C condition also allows the passage of current.

The invention will now be explained more fully by reference to the accompanying drawing showing, by way of example, one embodiment thereof.

A tube shown in Figure 1 comprises two control grids 2 and 3. The oscillations to be detected are supplied to the control grid 2 through a conductor 4. There is interposed between thecathode and control grid 2 a screen or accelerating grid 5- which, as long as the control grid 2, which is operated in class AB or B condition, does not allow the passage of current, conveys a substantially constant current. However, as soon as current is passed by the control grid 2, the current flowing to the grid 5 will rapidly decrease and attain a certain final value so that the voltage on this grid rises and assumes a pulse-like shape. The pulsatory voltage set up at grid 5 is supplied, via a retarding network 6, to the second control grid 3 of the tube I, which operates in class B or class 0 condition. The operation of the circuit 2 will now be explained more fully by reference to Fig.1.

In this figure the voltage set up at the grid 2 is designated a. This grid allows the passage of current at the moment I) so that the current flowing to the grid 5 and indicated by the curve 2' rapidly decreases and attains a final value 7'. Hence a pulsatory voltage is set up at this grid which is applied to the second control grid 3 of the tube a time t afterwards. The grid 3 will thus also pass current at the moment 0. Consequently, the tube i is only traversed by anode current between the moments c and d. The time ed, as may be seen from the figure, bears a linear relationship to the periodic time of the oscillations to be detected. The figure shows that, if the time t has a value somewhat smaller than half of the shortest momentary periodic time of the frequency-modulated incoming signal, the anode current of the tube I has a modulation depth or approximately Consequently, a high sensitivity may be ensured by including a resistance of sufficiently high value in the anode circuit of the tube l.

The present invention is not limited to the example shown in the figure and notably it is possible for the pulsatory voltage to be supplied to the grid 3 of tube I to be derived, for example, from the anode circuit of an auxiliary tube, whose control grid, which is adjusted in class AB or B, is supplied with the oscillations to be detected.

According to another solution, a pulsatory voltage is derived from a screen-grid following the grid 2 of tube I, which pulsatory voltage is supplied to a phase-inverting tube or transformer, whereupon the voltage inverted in phase opens the grid 3 of. tube 1 a constant time t later than the moment at which the grid 2 of tube l allows the passage of current.

What I, claim is:

1. A circuit arrangement for demodulating a source of frequency modulated signals comprising, a thermionic discharge tube having a oathode, anodefirst and second control grids and a screen electrode between the cathode and the first control grid, means to supply s urce of signais to the first control grid-cathode l-cuit of the said thermionic discharge tube :7 leans to derive a pulsed voltage at the-screen ectrode cathode circuit of the said thermionic discharge tube proportional to the modulation of the signals, said latter means comprising a source of bias voltage applied to the first control grid of the said thermionic discharge tube having a value at which first control grid current will flow for a time proportional to the modulation of the signal, a time delay network, and means to couple the screen electrode to the second control grid through the said time delay network.

2. A circuit arrangement for demodulating a source of frequency modulated signals comprising, a thermionic discharge tube having a cathode, anode, first and second control grids and a screen electrode between the cathode and the first control grid, means to supply the source of signals to the first control grid-cathode circuit of the said thermionic discharge tube, means to derive a pulsed voltage in the screen electrode cathode circuit of the said thermionic discharge tube proportional to the modulation of the signals, said latter means comprising a source of class B bias voltage applied. to the first control grid of the said thermionic discharge tube having a value at which first control grid current will flow for a time proportional to the modulation of the signal, a resistance-capacitance network, a source of class C bias voltage applied to the second control grid of the said second thermionic discharge tube, and means to couple the screen electrode to the second control grid through the said resistance-capacitance network.

3. A circuit arrangement for demodulating a source of frequency modulated signals comprising, a thermionic discharge tube having a cathode, anode, first and second control grids and a screen electrode between the cathode and the first control grid, means to supply the source of signals to the first control grid-cathode circuit of the said thermionic discharge tube, means to derive a pulsed voltage in the screen electrode cathode circuit of the said thermionic discharge tube proportional to the modulation of the signals and having a pulse duration less than one half a semicycle of the signals, said latter means comprising a source of class B bias voltage applied to the first control grid of the said thermionic discharge tube having a value at which first control grid current will fiow for a time proportional to the modulation of the signal, a resistance-capacitance network, a source of class B bias voltage applied to the second control grid of the said thermionic discharge tube, and means to couple the screen electrode to the second control grid through the said resistance-capacitance net- Work.

4. A circuit arrangement for detecting a frequency modulated wave, comprising a thermionic discharge tube having a cathode, an anode and first and second control grids interposed in the order named between the cathode and anode and having an accelerating electrode, means to apply the frequency modulated wave to said first control grid, means to apply biasing potentials to said first and second control grids to cut off electron current flow from the cathode to the anode through the said control grids for a time period less than a period of the mean frequency value of said frequency modulated wave, means to derive a pulsed voltage from said accelerating electrode, means to apply said pulsed voltage to said second control grid to render the same electron conductive a fixed time interval subsequent to electron conduction through said first control grid, and means to derive a de-- tected wave from said anode.

5. A circuit arrangement for detecting a frequency modulated wave, comprising a thermionic discharge tube having a cathode, an anode and first and second control grids interposed in the order named between the cathode and anode and having an accelerating electrode, means to apply the frequency modulated wave to said first control grid, means to apply a biasing potential to said first control grid to cut oil electron flow from the cathode to the anode through said first control grid for a time period within one half period of the mean frequency value of the frequency modulated wave, means to apply a biasing potential to said second control grid to cut oif electron current flow from the cathode to the anode through said second control grid for a time period between one-half period and a full period of the mean frequency value of the frequency modulated wave, means to derive a pulse voltage from said accelerating electrode, means to apply said pulse voltage to said second control grid to render the same electron conductive a fixed time interval subsequent to electron conduction through said first control grid, and means to derive a detected wave from said anode.

6. A circuit arrangement for detecting a frequency modulated wave, comprising a thermionic discharge tube having a cathode, an anode and first and second control grids interposed in the order named between the cathode and anode and having an accelerating electrode, means to apply the frequency modulated wave to said first control grid, means to apply a biasing potential to said first control grid to out ofi electron current flow from the cathode to the anode through said first control grid for a time period within one half period of the mean frequency value of the frequency modulated wave, means to apply a biasing potential to said second control grid to cut off electron current flow from the cathode to the anode through said second control grid for a time period between one half period and a full period of the mean frequency value of the frequency modulated wave, means to derive a pulse voltage from said accelerating electrode, means to apply said pulse voltage to said second control grid to render the same conductive a time interval equal to approximately one-half period of the highest frequency of said frequency modulated wave subsequent to electron conduction through said first control grid, and means to derive a detected wave from said anode.

ADRIANUS J OHANNES WILHELMUS MARIE VAN OVERBEEK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,087,429 Crosby July 20, 1937 2,239,757 Sanders Apr. 29, 1941 2,263,615 Crosby Nov. 25, 1941 2,284,444 Peterson May 26, 1942 2,296,090 Crosby Sept. 15, 1942 2,343,263 Orkrent Mar. 7, 1944 2,462,110 Levy Feb. 22, 1949 

